Superconducting photon detector

ABSTRACT

The various embodiments described herein include methods, devices, and systems for fabricating and operating superconducting photon detectors. In one aspect, a photon detector includes: (1) a first waveguide configured to guide photons from a photon source; (2) a second waveguide that is distinct and separate from the first waveguide and optically-coupled to the first waveguide; and (3) a superconducting component positioned adjacent to the second waveguide and configured to detect photons within the second waveguide.

RELATED APPLICATIONS

This application is a continuation of PCT International ApplicationSerial No. PCT/US2019/016885, filed Feb. 6, 2019, entitled“Superconducting Photon Detector,” which claims priority U.S.Provisional Application Ser. No. 62/627,115, filed Feb. 6, 2018, alsoentitled “Superconducting Photon Detector.” Each of these applicationsis hereby incorporated by reference in its entirety.

TECHNICAL FIELD

This relates generally to photon detectors, including but not limitedto, superconducting photon detectors.

BACKGROUND

Photon detectors are essential components in many electronic devices.Ultra-sensitive photon detectors that are capable of detecting a smallnumber of photons, such as individual photons (e.g., single photons),are used in a variety of applications, such as optical communications,medical diagnostics, and space research. One such use of ultra-sensitivephoton detectors is for optical quantum information applications.

Current crowding effects (e.g., due to a non-uniform shape) lead tolimitations in efficiency and yield of many conventional photondetectors. For example, current crowding may lead to a reduced currentdensity in some parts of the detector that create blind spots, andconversely lead to an increased current density in other parts of thedetector that can reduce the critical current of the detector, therebyimpacting performance and yield.

SUMMARY

There is a need for systems and/or devices with efficient and effectivemethods for detecting photons. Such systems, devices, and methodsoptionally complement or replace conventional systems, devices, andmethods for detecting photons.

Photon detectors typically include one or more electrical components togenerate an electrical signal in response to a received photon. Innanowire-based single photon detectors, current crowding due to thenon-uniform and/or non-straight nature of nanowires leads to limitationsin detection efficiency and/or yield. For example, in a hair-pinconfiguration, an overlap of the optical field with the tip of the hairpin nanowire results in lower detection efficiency due to thenon-uniform current distribution in the bend of the nanowire. Thenon-uniform current distribution in the bend of the nanowire leads to:(1) a reduced current density in some parts of the nanowire, whichcreates blind spots, and (2) an increased current density in other partsof the nanowire, which reduces the threshold current of the device,thereby impacting overall device performance.

The present disclosure describes photon detector systems and methodsthat utilize optically-coupled waveguides integrated with asuperconducting nanowire, which operates as a photon detection element.These systems and methods provide several advantages compared toconventional nanowire-based photon detectors: (1) they reduce oreliminate current crowding within superconducting nanowires; (2) theyreduce or eliminate blind spots in the superconducting nanowires; (3)they allow for accurate control of detection efficiency (e.g., thetransfer efficiency can be adjusted without changing the detectorgeometry); and (4) they are scalable to multi-element devices.

In some embodiments, using two waveguides separated by a gap, light iscoupled to only a uniform straight section of a waveguide integratedwith a nanowire detector. In some embodiments, the waveguides arearranged and sized so that light adiabatically transfers between thewaveguides. In some embodiments, the waveguides are arranged and sizedso that light evanescently transfers between the waveguides. In someembodiments, the widths of the two waveguides and the gap between thetwo waveguides is configured to allow light to efficiency andadiabatically couple from the input waveguide to the waveguidecontaining the nanowire detector. In accordance with some embodiments,as the light couples into the waveguide with the nanowire detector, itis absorbed by the nanowire resulting in the detection of an inputphoton.

In accordance with some embodiments, the waveguides are designed tocouple any preselected portion of the received light into the detector.In some embodiments, the amount of light coupled into the detector isbased on a length and gap of the coupler. In some embodiments, theamount of light coupled into the detector is based on the waveguidewidth and nanowire properties. In some embodiments, the waveguides areconfigured and/or positioned to couple light only toward a detectionzone (e.g., a narrow, straight section) of the nanowire. This reducesand/or avoids blind spots or absorption of light in detector areas withreduced detection efficiency.

In accordance with some embodiments, the multi-element detector is usedto enable the detection of multiple photons. In some embodiments, themulti-element detector is used to overcome a detection refresh timelimitation of a single detector element. In some embodiments, thecoupling efficiency for each detector is controlled to allow a uniformprobability of detection across all detector elements. For example, afirst detector element (or a waveguide integrated with the firstdetector element) has a weaker coupling efficiency than subsequentdetector elements (or waveguides respectively integrated with respectivesubsequent detector elements) to enable uniform probability ofabsorption across the multiple detector elements.

In one aspect, some embodiments include a photon detector having: (1) afirst waveguide configured to guide photons from a photon source; (2) asecond waveguide that is distinct and separate from the first waveguideand optically-coupled (e.g., adiabatically or evanescently) to the firstwaveguide; and (3) a superconducting component positioned adjacent tothe second waveguide and configured to detect photons within the secondwaveguide.

In another aspect, some embodiments include a method for detectingphotons, the method including: (1) receiving one or more photons from aphoton source; (2) directing the one or more photons through a firstwaveguide; (3) optically transferring at least one photon of the one ormore photons from the first waveguide to a second waveguide that isdistinct and separate from the first waveguide; and (4) detecting the atleast one photon within the second waveguide using a photon sensorpositioned adjacent to the second waveguide.

In yet another aspect, some embodiments include a method of fabricatinga photon detector, the method including: (1) providing a substrate; (2)depositing a layer of a waveguide material over the substrate; (3)adapting the layer of the waveguide material into a first waveguide anda second waveguide that is distinct and separate from the firstwaveguide; and (4) forming a photon sensor over the second waveguide.

In yet another aspect, some embodiments include a directional couplerdevice having: (1) a first photonic waveguide including a first regionand a second region that is distinct from and mutually exclusive to thefirst region of the first photonic waveguide, where: (a) the firstregion of the first photonic waveguide has a linear shape with a firstend and a second end that is opposite to the first end of the firstregion of the first photonic waveguide; and (b) the first region of thefirst photonic waveguide is configured to receive one or more photonstravelling from the first end of the first region of the first photonicwaveguide toward the second end of the first region of the firstphotonic waveguide; (2) a second photonic waveguide that is distinct andseparate from the first photonic waveguide, the second photonicwaveguide including a first region and a second region that is distinctfrom and mutually exclusive to the first region of the second photonicwaveguide, where: (a) the first region of the second photonic waveguideis linear in shape and positioned adjacent to the first region of thefirst photonic waveguide; (b) the first region of the second photonicwaveguide is a first distance from the first photonic waveguide, and thesecond region of the second photonic waveguide is a second distance tothe first photonic waveguide, that is greater than the first distance;(c) the first region of the second photonic waveguide has a first endand a second end that is opposite to the first end of the first regionof the second photonic waveguide; and (d) at least a subset of the oneor more photons transmitted from the first end of the first region ofthe first photonic waveguide toward the second end of the first regionof the first photonic waveguide is transferred to the second photonicwaveguide; and (3) a superconducting detector component having a firstportion and a second portion that is distinct from and mutuallyexclusive to the first portion of the superconducting component, where:(a) the first portion of the superconducting detector component islinear in shape and positioned adjacent to the first region of thesecond photonic waveguide; (b) the first portion of the superconductingdetector component spans the first region of the second photonicwaveguide; and (c) at least a portion of the first portion of thesuperconducting detector component transitions from a superconductingstate to a non-superconducting state in response to one or more incidentphotons transmitted from the first waveguide.

Thus, devices and systems are provided with methods for fabricating andoperating superconducting photodetector circuitry, thereby increasingthe effectiveness, efficiency, and user satisfaction with such systemsand devices.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the various described embodiments,reference should be made to the Detailed Description below, inconjunction with the following drawings in which like reference numeralsrefer to corresponding parts throughout the figures.

FIG. 1A is a schematic diagram illustrating current crowding effectswithin a non-linear wire in accordance with some embodiments.

FIG. 1B is a cross-sectional view of an example optical device inaccordance with some embodiments.

FIGS. 1C-1F are schematic diagrams illustrating representative opticaldevices in accordance with some embodiments.

FIG. 1G is a cross-sectional view of an example optical device inaccordance with some embodiments.

FIGS. 2A-2D are schematic diagrams illustrating a representativeoperating sequence of a representative optical device in accordance withsome embodiments.

FIGS. 3A-3B are cross-sectional views of example optical devices inaccordance with some embodiments.

FIGS. 4A-4B are schematic diagrams illustrating representativemulti-element optical detector systems in accordance with someembodiments.

FIG. 5 is a schematic diagram illustrating a representative opticalsystem in accordance with some embodiments.

Like reference numerals refer to corresponding parts throughout theseveral views of the drawings.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments, examples of whichare illustrated in the accompanying drawings. In the following detaileddescription, numerous specific details are set forth in order to providea thorough understanding of the various described embodiments. However,it will be apparent to one of ordinary skill in the art that the variousdescribed embodiments may be practiced without these specific details.In other instances, well-known methods, procedures, components,circuits, and networks have not been described in detail so as not tounnecessarily obscure aspects of the embodiments.

Many modifications and variations of this disclosure can be made withoutdeparting from its spirit and scope, as will be apparent to thoseskilled in the art. The specific embodiments described herein areoffered by way of example only, and the disclosure is to be limited onlyby the terms of the appended claims, along with the full scope ofequivalents to which such claims are entitled.

The present disclosure describes systems and devices that incorporatesuperconducting photon detector(s), such as superconducting nanowiresingle photon detectors (SNSPDs), in a waveguide coupler configuration(e.g., a directional coupler). In some embodiments, a superconductingnanowire is positioned adjacent to a detector waveguide that isoptically-coupled to an input waveguide to form a directional coupler(e.g., an asymmetric coupler due to the presence of the nanowire). Insome embodiments, the waveguides, and superconducting nanowire, aresized and positioned so that the coupling efficiency of the directionalcoupler exceeds 90%, 95%, or 99%.

Such systems and devices provide advantages when compared to theconventional detector-to-waveguide coupling schemes. For example, inaccordance various embodiments, the disclosed systems and devices: (1)reduce or eliminate current crowding effects within the nanowiredevices; (2) reduce or eliminate blind spots in the detector; (3) allowfor accurate control of coupling to the detector, e.g., the absorptionin the detector can be adjusted without changing the detector geometry;(4) are more robust towards drift and sidewall defects in the detectoras compared to conventional devices; (5) are scalable to multi-elementoptical detection systems; and (6) minimize back reflections due toindex of refraction changes within the waveguides.

A further advantage of the disclosed systems and devices is ease offabrication. In accordance with some embodiments, the disclosed systemsand devices reduce and/or eliminate bends in the active structure.Straight (linear) sections of nanowires are generally more accuratelyand consistently fabricated as compared to sections with bends orcurves, which can lead to irregularities, constrictions, defects, andthe like.

In some embodiments, an optical system includes a directional coupler(e.g., an asymmetric coupler) with an input waveguide and a detectorwaveguide separated by a gap (e.g., an air gap or dielectric gap), andwith the detector waveguide containing an integrated nanowire detector.In some embodiments, the integrated nanowire detector is on a same dieas the detector waveguide. For example, the integrated nanowire detectoris fabricated in a same process as the detector waveguide. In someembodiments, the waveguides are arranged and sized such that light isevanescently coupled to a uniform, straight section of the nanowiredetector via the two waveguides. Evanescent coupling (also sometimescalled “evanescent field coupling” or “evanescent wave coupling”) occurswhen waveguides are positioned so that the evanescent field generatedwithin one waveguide excites a wave in the other waveguide, leading totransmission of light between the waveguides. In some embodiments, thewaveguides are arranged and sized such that light is adiabaticallycoupled to a uniform, straight section of the nanowire detector via thetwo waveguides. Adiabatic coupling occurs when waveguides are positionedso that an optical mode within one waveguide transitions to an analogousmode within the other waveguide.

In some embodiments, the widths of the two waveguides, and optionallythe sizing of the gap between the two waveguides, are configured toallow light to optically couple from the input waveguide and into thedetector waveguide with high coupling efficiency (e.g., greater than90%, 95%, or 99%). In accordance with some embodiments, as the lightcouples into the detector waveguide, it is absorbed by the nanowiredetector resulting in a detection signal from the nanowire detector. Inaccordance with some embodiments, coupling the detector to the detectorwaveguide, rather than the input waveguide, reduces reflection ofphotons that travel via the waveguides. In some embodiments, the gapdistance between the waveguides is adjusted to reduce or minimize thereflection of photons within the waveguides and allow adiabatic couplingbetween the waveguides.

In accordance with some embodiments, an optical system is configured tocouple any preselected portion of the light from the input waveguideinto the detector. In some embodiments, the amount of light coupled intothe detector is based on a length and gap of the coupler. In someembodiments, the amount of light coupled into the detector is based onthe waveguide width and nanowire properties. In some embodiments, thewaveguides are configured and/or positioned to couple only to adetection zone (e.g., a narrow, straight section) of the nanowire.Coupling to the detection zone reduces and/or avoids blind spots orabsorption of light in detector areas with reduced detection efficiency.

In accordance with some embodiments, the multi-element detector is usedto enable the detection of multiple photons, as described in detailbelow with respect to FIGS. 4A-4B. In some embodiments, themulti-element detector is used to overcome a detection refresh timelimitation of a single detector element. In some embodiments, thecoupling efficiency for each detector is preset to allow a uniformprobability of detection across all detector elements. For example, afirst detector element is configured to have a weaker couplingefficiency than subsequent detector elements, thereby presenting auniform probability of absorption across the multiple detector elements.

As described below, the disclosed devices and system provide advantagesover conventional photon detectors. First, absorption of light only instraight sections of the nanowire detectors avoids currentredistribution issues that may lead to trade-offs in current density andphoto-sensitivity. Second, the amount of light coupled into the nanowiredetector is adjustable by changing a coupling length and/or a couplinggap distance (rather than adjusting parameters of the nanowire detectoritself). Thus, a same detector waveguide with an integrated nanowiredetector layout and design may be used for each detector element of amulti-element detector system, which eases design of the multi-detectorsystem and may reduce requirements for the electronic control andread-out circuitry. Third, the disclosed devices and system allow foradiabatic coupling to the nanowire detectors that, for example, reduceback reflection due to the impendence mismatch.

As used herein, a “superconducting” material is a material that iscapable of operating in a superconducting state (under particularconditions). For example, a superconducting material is a material thatoperates as a superconductor (e.g., operates with zero electricalresistance) when cooled below a particular temperature (e.g., a criticaltemperature) and having less than a maximum current flowing through it.A superconducting material is also called herein asuperconduction-capable material. The superconducting materials may alsooperate in an “off” state where little or no current is present. In someembodiments, the superconducting materials operate in anon-superconducting state during which the materials have a non-zeroelectrical resistance (e.g., a resistance in the range of one thousandto ten thousand ohms). For example, a superconducting material suppliedwith a current greater than a threshold superconducting current for thesuperconducting material may transition from a superconducting statewith zero electrical resistance to a non-superconducting state withnon-zero electrical resistance.

As used herein, a “wire” is a section of material configured fortransferring electrical current. In some embodiments, a wire includes asection of material conditionally capable of transferring electricalcurrent (e.g., a wire made of a superconducting material that is capableof transferring electrical current while the wire is maintained at atemperature below a critical temperature). A cross-section of a wire(e.g., a cross-section that is perpendicular to a length of the wire)optionally has a geometric (e.g., flat or round) shape or anon-geometric shape. In some embodiments, a length of a wire is greaterthan a width or a thickness of the wire (e.g., the length of a wire isat least 5, 6, 7, 8, 9, or 10 times greater than the width and thethickness of the wire).

FIG. 1A is a schematic diagram illustrating current crowding effectswithin a non-linear wire in accordance with some embodiments. FIG. 1Ashows a non-linear wire 180 (e.g., a wire with a hair-pin turn) withcurrent 181 flowing through the wire. As shown in FIG. 1A, thenon-linearity of the wire 180 results in current crowding along theinner radius of the turns in the wire 180 and potential blind spots 183along the outer radius of the turns. In implementations in which thewire 180 is utilized as a photon detector, photons incident to the blindspots 183 may not be detected.

For example, if the wire 180 is a superconducting wire, it has anassociated superconducting current density threshold. To operate as aphoton detector, the wire 180 may be coupled to a bias current that isconfigured to maintain the superconducting wire “just below” thesuperconducting current density threshold, such that energy from asingle photon is sufficient to transition the wire from asuperconducting state to a non-superconducting state. In this example,transitioning from the superconducting state to the non-superconductingstate is interpreted as detection of an incident photon. However,because the current density of the wire 180 is greater at the innerradius than the outer radius, the bias current is constrained by theinner radius density. Additional current density at the outer radiusgenerated from a photon incident to one of the blind spots 183 maytherefore be insufficient to cause the superconducting wire totransition from the superconducting state to the non-superconductingstate. Thus, photons incident to the blind spots may not be detected.

FIG. 1B is a cross-sectional view of an optical device 191 in accordancewith some embodiments. As shown in FIG. 1B, the optical device 191includes a waveguide 190 optically-coupled with a detector 192 (e.g., asuperconducting detector). The optical device 191 further includeslayers 194 and 195 (e.g., dielectric layers) that cover the top andbottom of the waveguide 190 and the detector 192. In some embodiments,layers 194 and 195 serve as the upper cladding and lower cladding,respectively, of the waveguide 190, e.g., the index of refraction of thelayers 194 and 195 is lower than the index of refraction of thewaveguide 190. However, in the region of the waveguide 190 that includesdetector 192, the index of refraction profile in the upper cladding ismodified slightly from its bulk value due to the presence of the thindetector layer that is interposed between layer 194 and waveguide 190.As a result, photons 196 that originally propagate in the waveguide 190experience an abrupt change in refractive index when they encounter thedetector layer region and can be partially reflected (i.e., some of theinput light from photons 196 can be back reflected as reflection 198).Accordingly, some of the photons 196 that were initially propagating inthe waveguide 190 cannot enter the region of the waveguide that includesdetector 192 (because they are back reflected). Thus the efficiency ofoptical device 191 is lowered (e.g., fewer photons 199 are able to beabsorbed by detector layer 192). Utilizing a directional couplerconfiguration (e.g., as described with below respect to FIGS. 1C-1F)reduces, or minimizes, reflections due to changes in the index ofrefraction.

FIGS. 1C-1F are schematic diagrams illustrating representative opticaldevices in accordance with some embodiments. FIG. 1C shows an opticaldevice 100 including a first waveguide 102 in proximity with a secondwaveguide 104. In accordance with some embodiments, the waveguides 102and 104 are optically coupled (e.g., evanescently or adiabatically). Inoptically-coupled waveguides, photons transfer between the waveguides asrepresented by arrows 106. In some embodiments, the waveguides 102 and104 are phase matched. FIG. 1C further shows photons 119 traveling fromposition 119-a in waveguide 102 to position 119-b in waveguide 104 viathe optical coupling 106. In some embodiments, the gap 111 between thewaveguides is configured to provide a particular transfer rate betweenthe waveguides 102 and 104 (e.g., between 0% and 100%). For example, thegap 111 is between 100 nanometers and 500 nanometers. In someembodiments, the length 109 of a region of the waveguide 102 inproximity to the waveguide 104 is configured to provide a particulartransfer rate (e.g., in addition to, or alternatively to, selecting thegap 111). For example, the length 109 is between 1 micron and 100microns. In some embodiments, the waveguides 102 and 104 have respectivewidths between 250 nanometers and 1000 nanometers. In some embodiments,the waveguides 102 and 104 have respective heights between 100nanometers and 1 micron. In some embodiments, the waveguides 102 and 104are composed of silicon. In some embodiments, the waveguides 102 and 104include silicon (e.g., silica, silicon oxynitride, etc.). In someembodiments, the waveguides 102 and 104 include germanium.

FIG. 1D shows the optical device 100 of FIG. 1C with the addition of asuperconducting component 108 coupled to the waveguide 104. FIG. 1Dfurther shows the first waveguide 102 having a region 101 that islocated at a distance 103 from a region 115 of the second waveguide 104and a region 105 that is located at a distance 107 from a region 113 ofthe second waveguide 104. FIG. 1D also shows the superconductingcomponent 108 having a portion 117 adjacent to the region 113 of thesecond waveguide 104. Optionally, the portion 117 of the superconductingdetector component adjacent to region 113 is vertically stacked withregion 113 of the second waveguide 104, for example as shown in FIG. 3B.In some embodiments, the portion 117 of the superconducting component108 is in contact with the region 113 of the waveguide 104. In someembodiments, the portion 117 of the superconducting component 108 isseparated from the region 113 of the waveguide 104 by one or moredielectric layers. In some embodiments, a thickness of the one or moredielectric layers is below a threshold thickness so that the portion 117of the superconducting component 108 is capable of detecting one or morephotons passing through, or received by, the region 113 of the waveguide104. In some embodiments, as shown in FIG. 1D, the superconductingcomponent 108 is aligned (e.g., directly across from) the region 105,while in other embodiments, the superconducting component 108 is offset(e.g., shifted to the left or right) from the region 105. In someembodiments, the superconducting component 108 is arranged and sized soas to prevent optical coupling between the ends of the superconductingcomponent 108 and the waveguide 102. In some embodiments, the length ofthe portion 117 is sufficiently larger than the region 105 to preventoptical coupling between the ends of the superconducting component 108and the waveguide 102.

In accordance with some embodiments, a directional couplingconfiguration is utilized in FIG. 1D to reduce, or minimize, reflectionswithin the waveguides, e.g., such as back reflections as lightencounters an abrupt change in an index of refraction. Reflections arereduced by using a directional coupling. In some embodiments, a couplingcoefficient between the waveguide 102 and the waveguide 104 is dependenton the distance 107 and the length of region 105. In some embodiments,the length of the region 105 and the coupling distance 107 are selectedto achieve a desired coupling coefficient. In some embodiments, thedistance 107 and/or the length of region 105 is adjusted to change acoupling efficiency between the waveguides. In some embodiments, thesuperconducting component 108 is arranged and sized such that an indexof refraction between the regions 105 and 113 is constant.

FIG. 1E shows the optical device 100 of FIG. 1C with the addition of asuperconducting component 110 coupled to the waveguide 104. Thesuperconducting component 110 in FIG. 1E includes a detection zone 112configured to detect photons within the waveguide 104 (e.g., photonstransferring from the waveguide 102). In some embodiments, thesuperconducting components 108 and 110 comprise superconductingnanowires. In some embodiments, the detection zone 112 comprises astraight, uniform region such a superconducting threshold currentdensity for the detection zone is constant throughout the detection zone112. In some embodiments, the detection zone 112 is configured to reduceor eliminate blind spots. In some embodiments, the non-detectingportions of the detectors vary in shape and size (e.g., have roundedcorners and/or other geometric and non-geometric shapes). In someembodiments, the superconducting components 108 and 110 are configuredso as to detect single photons received by the waveguide 104 (e.g.,detect a single photon at a particular time). In some embodiments, thesuperconducting components 108 and 110 are configured so as to detect athreshold amount of photons (e.g., 10, 20, or 100 photons). Line AA′ inFIG. 1E represents a plane upon which the cross-sectional view shown inFIG. 3A is taken. In some embodiments, the superconducting components108 and 110 have respective detection widths between 10 nanometers and200 nanometers. For example, the superconducting component 110 haswidths between 200 nanometers and 2 microns with the detection zone 112having a width between 10 nanometers and 200 nanometers. In someembodiments, the superconducting components 108 and 110 have respectiveheights between 3 nanometers and 10 nanometers. In some embodiments, thesuperconducting component 110 is arranged and sized so as to preventoptical coupling between the non-detecting portions of thesuperconducting component 110 and the waveguide 102.

FIG. 1F shows the optical device of FIG. 1E with the addition of readoutcircuitry 130 and a current source 132 coupled to the superconductingcomponent 110 via contacts 120. In some embodiments, the contacts 120are electrically-conductive (e.g., are composed of gold, copper, or thelike). In some embodiments, the readout circuitry 130 comprises one ormore superconducting components. In some embodiments, the readoutcircuitry 130 is configured to determine when the superconductingcomponent 110 is in a non-superconducting state. In some embodiments,the readout circuitry 130 is configured to determine when thesuperconducting component 110 has received a threshold number ofphotons. In some embodiments, the readout circuitry 130 is configured tomeasure a portion of current received from the current source 132. Insome embodiments, the readout circuitry 130 is separated from thecurrent source 132 by one or more resistors, such that a thresholdamount of current from the current source 132 only flows through thereadout circuitry 130 when the superconducting component 110 is in anon-superconducting state (e.g., in response to receiving a thresholdamount of photons). In some embodiments, the readout circuitry 130 iscoupled in parallel with the superconducting component 110, while inother embodiments, the readout circuitry 130 is coupled in series withthe superconducting component 110 (e.g., and is configured to determinea voltage drop associated with the superconducting component 110). Insome embodiments, (not shown) a voltage source is coupled to thesuperconducting component 110 (e.g., in addition to, or alternativelyto, the current source 132). Additional details regarding operation andreadout of photon detectors can be found in U.S. patent application Ser.No. 16/028,293, filed Jul. 5, 2018, entitled “Gated SuperconductingPhoton Detector.”

Although FIG. 1F shows readout circuitry 130 and current source 132coupled to the superconducting component 110, in some embodiments, thereadout circuitry 130 and current source 132 are coupled to a differentsuperconducting component, such as superconducting component 108 in FIG.1D.

FIG. 1G is a cross-sectional view of an optical device 171 in accordancewith some embodiments. The optical device 171 includes an inputwaveguide 172 that is optically-coupled with a detector waveguide 174,e.g., forming a directional coupler device. In accordance with someembodiments, the waveguides 172 and 174 are tapered (e.g., to promoteadiabatic coupling between the waveguides). A detector 176 (e.g., asuperconducting detector) is optically-coupled to the detector waveguide174. In accordance with some embodiments, photons 179 from a photonicsource travel through the waveguide 172 until at least a portion of thephotons 179 transfer to the waveguide 174 (e.g., adiabaticallytransfer). In accordance with some embodiments, the photons thattransfer to the waveguide 174 are detected by the detector 176 (e.g.,cause the detector 176 to transition from a superconducting mode to anon-superconducting mode). In some embodiments, the regions of thewaveguides 172 and 174 that are optically-coupled are tapered and one ormore other regions are not tapered. In some embodiments, the waveguides172 and 174 are arranged such that a distance between the taperedregions is constant (e.g., the distance between the tapered regionsvaries by less than 2%, 5%, or 10%, from a nominal or mean distancebetween the tapered regions). In some embodiments, (not shown) thewaveguides 172 and 174 are arranged such that a distance between thetapered regions varies along their lengths. In some embodiments, thedetector 176 includes a linear region with a length that exceeds a widthof the optically-coupled region of the waveguide 174 (e.g., to reducecurrent crowding effects within the detector).

FIGS. 2A-2D are schematic diagrams illustrating a representativeoperating sequence of an optical device 200 in accordance with someembodiments. The optical device 200 includes a first waveguide 102having a region in proximity to a second waveguide 104 such that thewaveguides 102 and 104 are optically coupled. The optical device 200further includes a superconducting component 201 having a detection zone203. In some embodiments, the superconducting component 201 correspondsto the superconducting component 108 or the superconducting component110. In the example illustrated in FIGS. 2A-2D the superconductingcomponent 201 is offset along the y-axis from a center of the waveguide104 to illustrate the photon 202 moving to the waveguide 104 (FIG. 2C)prior to being detected by the superconducting component 201 (FIG. 2D).In some embodiments, the superconducting component 201 is adjacent to acenter of the waveguide 104 along the y-axis. In some embodiments, thesuperconducting component 201 has a detection zone 203 that spans thewaveguide 104 along the y-axis.

FIG. 2A further shows the optical device 200 at a first time with aphoton 202 at a first position 202-a in the waveguide 102. FIG. 2B showsthe optical device 200 at a second time, subsequent to the first time,with the photon 202 transferring at position 202-b to the waveguide 104.FIG. 2C shows the optical device 200 at a third time, subsequent to thesecond time, with the photon 202 at a third position 202-c in thewaveguide 104. FIG. 2D shows the optical device 200 at a fourth time,subsequent to the third time, with the photon 202 contacting thesuperconducting component 201 at a position 202-d within the detectionzone 203. In accordance with some embodiments, the detection zone 203transitions from a superconducting state to a non-superconducting statein response to receiving the photon 202. In accordance with someembodiments the transition of the detection zone 203 causes a change inelectrical properties (e.g., a change in a current or voltage) at areadout circuit (e.g., readout circuitry 130).

FIGS. 3A-3B are cross-sectional views of example optical devices inaccordance with some embodiments. FIG. 3A illustrates an optical device300 having a first waveguide 102 adjacent to the second waveguide 104 ona substrate 302. For example, in FIG. 3A, the first waveguide 102 andthe second waveguide 104 are located on a same plane that is parallel tothe substrate 302. FIG. 3A further illustrates a superconductingcomponent 301 (or portion thereof, such as portion 117, as shown in FIG.1D) positioned above (e.g., on top of, or vertically stacked with) thesecond waveguide 104 (or a region thereof, such as region 113, as shownin FIG. 1D). In some embodiments, (not shown) the superconductingcomponent 301 is positioned on a side of the second waveguide 104. Insome embodiments, the superconducting component 301 corresponds to thesuperconducting component 108 or 110. In some embodiments, thewaveguides 102 and 104 have a same height and width. In someembodiments, the waveguides 102 and 104 have differing heights and/ordiffering widths.

In some embodiments, the first waveguide 102 and the second waveguide104 are separated by an air gap. In some embodiments, the firstwaveguide 102 and the second waveguide 104 are separated by a dielectricand/or insulating material. In some embodiments, the substrate 302 iscomposed of silicon or a silicon oxide.

FIG. 3B illustrates an optical device 310 having a first waveguide 102adjacent to the second waveguide 104. For example, in FIG. 3B, thewaveguide 102 is located under (e.g., beneath) the waveguide 104. FIG.3B further illustrates the waveguide 102 separated from the waveguide104 by an insulator 304 (e.g., silicon oxide), and the superconductingcomponent 301 adjacent to the waveguide 104 (e.g., the superconductingcomponent 301 is over (e.g., on top of) the waveguide 104). In someembodiments, the superconducting component 301 is located on a side ofthe waveguide 104. In some embodiments, the waveguide 102 is locatedover the waveguide 104 (e.g., the waveguide 102 is separated from thewaveguide 104 by an insulator 304) and a superconducting component 301is located under (e.g., beneath), or on a side of, the waveguide 104. Insome embodiments, the waveguides 102 and 104 have a same height andwidth. In some embodiments, the waveguides 102 and 104 have differingheights and/or differing widths.

FIGS. 4A-4B are schematic diagrams illustrating representativemulti-element detector systems in accordance with some embodiments. FIG.4A shows an optical system 400 having a first waveguide 402, additionalwaveguides 404-1 and 404-2, and superconducting components 408 (e.g.,408-1 and 408-2). FIG. 4B shows an optical system 420 having a firstwaveguide 402, additional waveguides 404 (e.g., 404-1 through 404-5),and superconducting components 408 (e.g., 408-1 through 408-5). AlthoughFIG. 4B shows the optical system 420 having 5 superconducting components408 and 5 additional waveguides 404, in various embodiments, the opticalsystem 420 has any preselected number of superconducting components 408and additional waveguides 404 (e.g., 3, 10, or 50 of each).

In accordance with some embodiments, photons in the waveguide 402transfer to the waveguides 404 and are detected at the correspondingsuperconducting components 408. In some embodiments, each waveguide 404is positioned at an equal distance from the waveguide 402, while inother embodiments, at least a subset of the waveguides 404 arepositioned at distinct distances from the waveguide 402 (e.g., each hasa distinct gap 111 associated with it). In some embodiments, eachwaveguide 404 has a same length 109, while in other embodiments, atleast a subset of the waveguides 404 have distinct lengths. In someembodiments, the waveguide 402 and each waveguide 404 are configuredand/or arranged such that there is a preset transfer rate associatedwith the waveguide 404. For example, the waveguides 402 and 404 in FIG.4A may be configured and/or arranged such that 50% of photons in thewaveguide 402 transfer to the waveguide 404-1 and the remaining 50% ofphotons in the waveguide 402 transfer to the waveguide 404-2. As anotherexample, the waveguides 402 and 404 in FIG. 4A may be configured and/orarranged such that 10% of photons in the waveguide 402 transfer to thewaveguide 404-1 and 70% transfer to the waveguide 404-2. In someembodiments, the superconducting components 408 are essentiallyidentical (e.g., the superconducting components 408 have a same shape ofthe superconducting component 108), whereas in other embodiments, atleast a subset of the superconducting components 408 are distinct fromone another (e.g., the superconducting components 408 have distinctshapes). For example, one or more of the superconducting components 408may have a shape similar to the superconducting component 108 whileother superconducting components 408 have a shape similar to thesuperconducting component 110.

FIG. 5 is a schematic diagram illustrating an optical system 500 inaccordance with some embodiments. The optical system 500 includes awaveguide 502 (e.g., an input waveguide), a waveguide 504 (e.g., a ringresonator), and a waveguide 506 (e.g., a detector waveguide). Thewaveguide 506 includes a superconducting detector 508 (e.g., one of thesuperconducting components 108, 110, or 201). In some embodiments, thesuperconducting detector 508 is integrated with the waveguide 506. Insome embodiments, the waveguide 504 is optically-coupled to thewaveguide 502 and the waveguide 506. In some embodiments, the waveguide504 is a closed waveguide loop forming a circular, elliptical, or otherloop configuration. In some embodiments, the waveguide 504 is configuredto have lossless bends (e.g., configured to have lossless bend radii).

In the example illustrated in FIG. 5, a photon 520 is provide along thewaveguide 502. The photon 520 adiabatically transfers from the waveguide502 to the waveguide 504 (e.g., with a transfer rate of 100%). Aftertransferring, the photon 520 travels along the waveguide 504 until itadiabatically transfers from the waveguide 504 to the waveguide 506.After transferring to the waveguide 506, the photon is absorbed by thesuperconducting detector 508 resulting in an electrical signal that isprovided to a readout circuit (e.g., readout circuitry 130, FIG. 1F)electrically coupled to the detector.

In light of these principles and embodiments, we now turn to certainadditional embodiments.

In accordance with some embodiments, a photon detector includes: (1) afirst waveguide (e.g., the waveguide 102, FIG. 1D) configured to guidephotons from a photon source; (2) a second waveguide (e.g., thewaveguide 104, FIG. 1D) that is distinct and separate from the firstwaveguide and optically-coupled to the first waveguide; and (3) asuperconducting component (e.g., the superconducting component 108, FIG.1D) positioned adjacent to the second waveguide and configured to detectphotons within the second waveguide. In some embodiments, the first andsecond waveguides are composed of a dielectric material, such assilicon. In some embodiments, the second waveguide includes an opticallyactive region, and the superconducting component is positioned adjacentto the optically active region.

In some embodiments, the superconducting component is positionedadjacent to a region of the second waveguide that is optically coupledto the first waveguide.

In some embodiments, the superconducting component detects photons inpart by transitioning from a superconducting state to anon-superconducting state in response to receiving light having anintensity above a threshold intensity.

In some embodiments, the superconducting component comprises a straightnanowire (e.g., corresponding to the detection zone 112, FIG. 1E). Insome embodiments, the nanowire comprises a superconducting material suchas niobium or a niobium alloy. In some embodiments, the nanowire has awidth in the range of 10 nm-200 nm. In some embodiments, the nanowirehas a length in the range of 1 micron to 100 microns. In someembodiments, the nanowire has a thickness in the range of 3 nm-10 nm.

In some embodiments, the detector further includes one or moreelectrical contacts (e.g., the contacts 120, FIG. 1F)electrically-connected to the superconducting component. In someembodiments, the electrical contacts comprise metal pads, such as goldor titanium gold metal pads. In some embodiments, the one or moreelectrical contacts have respective widths greater than a width of thelinear superconducting component.

In some embodiments, the superconducting component is adapted to have auniform current density. In some embodiments, the superconductingcomponent is adapted to have a uniform current density in a detectionzone of the superconducting component (e.g., the detection zone of thesuperconducting component is a straight wire).

In some embodiments, the first waveguide and the second waveguide arephase matched. In some embodiments, phase matching the first and secondwaveguides includes adjusting a width of the first waveguide, such thatit has a larger or narrower width than the second waveguide. In someembodiments, phase matching the first and second waveguides includesadjusting a width of the second waveguide, such that it has a larger ornarrower width than the first waveguide. In some embodiments, the firstwaveguide has a first width and the second waveguide has a second widththat is different from (e.g., larger or narrower) the first width (sothat the first waveguide is phase matched to the second waveguideintegrated with the superconducting component).

In some embodiments, the first waveguide and the second waveguide areconfigured to enable light to adiabatically transfer from the firstwaveguide to the second waveguide. For example, the first and secondwaveguides are configured such that 100% of the light in the firstwaveguide is transferred to the second waveguide. For example, the firstand second waveguides are configured such that more than 90%, 91%, 92%,93%, 94%, 95%, 96%, 97%, 98%, 99%, or 99.9% of the light in the firstwaveguide is transferred to the second waveguide.

In some embodiments, the first waveguide and the second waveguide areconfigured to have a preset light transfer rate between the first andsecond waveguides. In some embodiments, the preset light transfer rateis in the range of 100% to 1%.

In some embodiments, the detector further including: (1) a thirdwaveguide (e.g., waveguide 404-2, FIG. 4A) that is distinct and separatefrom the first waveguide and optically coupled to the first waveguide;and (2) a second superconducting component (e.g., superconductingcomponent 408-2, FIG. 4A) positioned adjacent to the third waveguide andconfigured to detect photons within the third waveguide. In someembodiments, the third waveguide is distinct and separate from and thesecond waveguide. In some embodiments, the second superconductingcomponent is distinct and separate from the superconducting component.

In some embodiments, the first waveguide and the second waveguide arelocated on a same horizontal plane (e.g., as illustrated in FIG. 3A). Insome embodiments, the first waveguide is located next to the secondwaveguide.

In some embodiments, the first waveguide is located on a firsthorizontal plane and the second waveguide is located on a secondhorizontal plane that is distinct and separate from the first horizontalplane (e.g., as illustrated in FIG. 3B). In some embodiments, the firstwaveguide is located over or under the second waveguide. In someembodiments, the superconducting component is a linear superconductingcomponent.

In accordance with some embodiments, a method for detecting photonsincludes: (1) receiving one or more photons from a photon source; (2)directing the one or more photons through a first waveguide (e.g., asillustrated in FIG. 2A); (3) transferring (e.g., adiabatically orevanescently) at least one photon of the one or more photons from thefirst waveguide to a second waveguide that is distinct and separate fromthe first waveguide (e.g., as illustrated in FIG. 2B); and (4) detectingthe at least one photon within the second waveguide using a photonsensor positioned adjacent to the second waveguide (e.g., as illustratedin FIG. 2D).

In some embodiments, transferring at least one of the photons from thefirst waveguide to the second waveguide comprises optically transferringa preset ratio (e.g., a percentage) of the one or more photons to thesecond waveguide (e.g., 5%, 10%, 50%, 99%, or 100%).

In some embodiments: (1) the photon sensor includes a superconductingcomponent (e.g., the superconducting component 201, FIG. 2A); and (2)detecting the at least one photon using the photon sensor comprisesdetecting the at least one photon based on a transition of thesuperconducting component, triggered by the at least one photon, from asuperconducting state to a non-superconducting state. In someembodiments, the superconducting component is adapted to have a uniformcurrent density (e.g., by having a linear shape or by avoiding a bend).

In accordance with some embodiments, a method of fabricating a photondetector includes: (1) providing a substrate; (2) depositing a layer ofa waveguide material over the substrate; (3) adapting the layer of thewaveguide material into a first waveguide and a second waveguide that isdistinct and separate from the first waveguide; and (4) forming a photonsensor over the second waveguide.

In accordance with some embodiments, a method of fabricating a photondetector includes: (1) providing a substrate (e.g., the substrate 302,FIG. 3B); (2) depositing a first layer of a waveguide material (e.g.,corresponding to the waveguide 102, FIG. 3B) over the substrate; (3)adapting the first layer of the waveguide material into a firstwaveguide; (4) depositing a second layer of a waveguide material (e.g.,corresponding to the waveguide 104, FIG. 3B) over at least the firstwaveguide; (5) adapting the second layer of the waveguide material intoa second waveguide that is distinct and separate from the firstwaveguide; and (6) forming a photon sensor over the second waveguide(e.g., the superconducting component 301, FIG. 3B).

In some embodiments, forming the photon sensor includes: (1) depositinga layer of a superconducting material over at least the secondwaveguide; and (2) adapting the layer of the superconducting materialinto a superconducting component.

In accordance with some embodiments, a method of fabricating a photondetector includes: (1) providing a substrate; (2) depositing a firstlayer of a waveguide material over the substrate; (3) adapting the firstlayer of the waveguide material into a first waveguide; (4) depositing asecond layer of a waveguide material over the first layer; (5) adaptingthe second layer of the waveguide material into a second waveguide; (6)depositing a third layer over the second layer; and (7) adapting thethird layer into a photon sensor.

In some embodiments, a method includes: (1) providing a substrate; (2)depositing a first layer on the substrate; (3) adapting the first layerinto a photon sensor; (4) depositing a second layer on the first layer;(5) adapting the second layer into a first waveguide; (6) depositing athird layer on the second layer; and (7) adapting the third layer into asecond waveguide.

In some embodiments, adapting the third layer comprises removing one ormore portions of the third layer to define a nanowire. In someembodiments, the third layer comprises a layer of a superconductingmaterial.

In some embodiments, each waveguide material comprises a dielectricmaterial. In some embodiments, the first layer of a waveguide materialincludes a first dielectric material, and the second layer of awaveguide material includes a second dielectric material. In someembodiments, the first dielectric material is distinct from the seconddielectric material. In some embodiments, the first dielectric materialis essentially identical to the second dielectric material.

In some embodiments, the first waveguide and the second waveguide areconfigured to have a preset light transfer rate between the first andsecond waveguides. In some embodiments, the preset light transfer rateis based on a length of a section of the first waveguide that isadjacent to the second waveguide (e.g., the length 109, FIG. 1C).

In some embodiments, the method further includes adjusting the presetlight transfer rate by adjusting the length of the section of the firstwaveguide that is adjacent to the second waveguide. In some embodiments,the method further includes phase matching the first waveguide and thesecond waveguide (e.g., by adjusting a width and/or length of the firstwaveguide, and/or adjusting a gap between the waveguides).

In some embodiments, phase matching the first waveguide and the secondwaveguide includes adjusting one or more dimensions of the firstwaveguide and/or one or more dimensions of the second waveguide. In someembodiments, phase matching the first waveguide and the second waveguideincludes adjusting a width of the first waveguide and/or a width of thesecond waveguide. In some embodiments, phase matching the firstwaveguide and the second waveguide includes adjusting a height of thefirst waveguide and/or a height of the second waveguide.

In accordance with some embodiments, a photon detector device includes:(1) a first photonic waveguide (e.g., the waveguide 102, FIG. 1D)including a first region (e.g., the region 105) and a second region thatis distinct from and mutually exclusive to the first region of the firstphotonic waveguide, the first region of the first photonic waveguidehaving a first end and a second end that is opposite to the first end ofthe first region of the first photonic waveguide, where the first regionof the first photonic waveguide is configured to receive one or morephotons from the first end of the first region of the first photonicwaveguide toward the second end of the first region of the firstphotonic waveguide; (2) a second photonic waveguide (e.g., the waveguide104, FIG. 1D) that is distinct and separate from the first photonicwaveguide, the second photonic waveguide including a first region (e.g.,the region 113) and a second region that is distinct from and mutuallyexclusive to the first region of the second photonic waveguide, thefirst region of the second photonic waveguide being adjacent to thefirst region of the first photonic waveguide and having a first distance(e.g., the distance 107) to the first photonic waveguide, the secondregion (e.g., the region 115) of the second photonic waveguide having asecond distance (e.g., the distance 103), to the first photonicwaveguide, that is greater than the first distance, the first region ofthe second photonic waveguide having a first end and a second end thatis opposite to the first end of the first region of the second photonicwaveguide, whereby at least a subset of the one or more photonstransmitted from the first end of the first region of the first photonicwaveguide toward the second end of the first region of the firstphotonic waveguide is transferred to the second photonic waveguide(e.g., the first region of the second photonic waveguide); and (3) asuperconducting component (e.g., superconducting component 108, FIG. 1D)having a first portion (e.g., the portion 117) and a second portion thatis distinct from and mutually exclusive to the first portion of thesuperconducting component, the first portion of the superconductingcomponent being adjacent to the first region of the second photonicwaveguide and extending from a first position adjacent to the first endof the first region of the second photonic waveguide (e.g., the firstposition is located above the first end of the first region of thesecond photonic waveguide) toward a second position adjacent to thesecond end of the first region of the second photonic waveguide (e.g.,the second position is located above the second end of the first regionof the second photonic waveguide), whereby the first portion of thesuperconducting component transitions from a superconducting state to anon-superconducting state in response to one or more photons above apreselected detection threshold being transmitted through at least aportion of the first region of the second photonic waveguide. In someembodiments, the first and second photonic waveguides are composed of adielectric material, such as silicon. In some embodiments, at least oneof the first coupling region and the second coupling region has atapered width (e.g., as illustrated in FIG. 1G).

In some embodiments, the first portion of the superconducting componenthas a substantially linear shape (e.g., as illustrated by the portion117 in FIG. 1D). In some embodiments, the first portion of thesuperconducting component is linear. In some embodiments, the firstportion of the superconducting component does not have a bend that isless than 120 degrees. In some embodiments, the first portion of thesuperconducting component does not have a bend that is less than 90degrees. In some embodiments, the first portion of the superconductingcomponent does not have a bend that is greater than 240 degrees. In someembodiments, the first portion of the superconducting component does nothave a bend that is greater than 270 degrees. In some embodiments, thesuperconducting component has one or more portions (e.g., outside thefirst portion) that are not linear (e.g., superconducting component 108shown in FIG. 1D has two right angle corners extending from portion117).

In some embodiments, the first region of the first photonic waveguidehas a substantially linear shape (e.g., as illustrated by the region 105in FIG. 1D). In some embodiments, the first region of the first photonicwaveguide is linear. In some embodiments, the first region of the firstphotonic waveguide does not have a bend that is less than 120 degrees.In some embodiments, the first region of the first photonic waveguidedoes not have a bend that is less than 90 degrees. In some embodiments,the first region of the first photonic waveguide does not have a bendthat is greater than 240 degrees. In some embodiments, the first regionof the first photonic waveguide does not have a bend that is greaterthan 270 degrees. In some embodiments, the first photonic waveguide hasone or more regions that are not linear (e.g., first waveguide 102 inFIG. 1D has bends outside the first region).

In some embodiments, the first region of the second photonic waveguidehas a substantially linear shape (e.g., as illustrated by the region 113in FIG. 1D). In some embodiments, the first region of the secondphotonic waveguide is linear. In some embodiments, the first region ofthe second photonic waveguide does not have a bend that is less than 120degrees. In some embodiments, the first region of the second photonicwaveguide does not have a bend that is less than 90 degrees. In someembodiments, the first region of the second photonic waveguide does nothave a bend that is greater than 240 degrees. In some embodiments, thefirst region of the second photonic waveguide does not have a bend thatis greater than 270 degrees. In some embodiments, the second photonicwaveguide has one or more regions that are not linear (e.g., outside thefirst region).

In some embodiments, the first region of the second photonic waveguideis longer than the first region of the first photonic waveguide (e.g.,the region 113 is longer than the region 105 in FIG. 1D). In someembodiments, the first portion of the superconducting component islonger than the first region of the first photonic waveguide. In someembodiments, the first portion of the superconducting component has asubstantially same length as the first region of the second photonicwaveguide.

In some embodiments, the first region of the first photonic waveguide isphase matched with the first region of the second photonic waveguide incombination with the first portion of the superconducting component.

In some embodiments, the first region of the first photonic waveguidehas a first width and the first region of the second photonic waveguidehas a second width that is less than the first width. For example, awidth of the region 113 in FIG. 1D is less than a width of the region105 in accordance with some embodiments.

In some embodiments, (1) the first portion of the superconductingcomponent is located over the first region of the second photonicwaveguide; (2) the first position is located over the first end of thefirst region of the second photonic waveguide; and (3) the secondposition is located over the second end of the first region of thesecond photonic waveguide.

In some embodiments, the superconducting component extends beyond thesecond position (e.g., the superconducting component extends beyond thesecond end of the first region of the second photonic waveguide). Insome embodiments, the first portion of the superconducting component islonger than the first region of the second photonic waveguide.

In some embodiments, a first layer includes both the first region of thefirst photonic waveguide and the first region of the second photonicwaveguide (e.g., as illustrated in FIG. 3A). In some embodiments, thefirst region of the first photonic waveguide is positioned side-by-sidewith the first region of the second photonic waveguide. In someembodiments, the first region of the second photonic waveguide ispositioned over the first region of the first photonic waveguide (e.g.,as illustrated in FIG. 3B).

In some embodiments, the first region of the first photonic waveguide ispositioned over the first region of the second photonic waveguide andthe first region of the second photonic waveguide is positioned over thefirst portion of the superconducting component.

In some embodiments, the detector device further includes a readoutcircuit (e.g., readout circuitry 130, FIG. 1F) configured to measure aresistance, or impedance, of at least the first portion of thesuperconducting component (e.g., the readout circuit is configured tomeasure a resistance of the superconducting component).

In some embodiments, the detector further includes a current source(e.g., the current source 132, FIG. 1F) configured to provide a firstcurrent to at least the first portion of the superconducting component.

It will also be understood that, although the terms first, second, etc.are, in some instances, used herein to describe various elements, theseelements should not be limited by these terms. These terms are only usedto distinguish one element from another. For example, a first waveguidecould be termed a second waveguide, and, similarly, a second waveguidecould be termed a first waveguide, without departing from the scope ofthe various described embodiments. The first waveguide and the secondwaveguide are both waveguides, but they are not the same waveguideunless explicitly stated as such.

The terminology used in the description of the various describedembodiments herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used in thedescription of the various described embodiments and the appendedclaims, the singular forms “a”, “an” and “the” are intended to includethe plural forms as well, unless the context clearly indicatesotherwise. It will also be understood that the term “and/or” as usedherein refers to and encompasses any and all possible combinations ofone or more of the associated listed items. It will be furtherunderstood that the terms “includes,” “including,” “comprises,” and/or“comprising,” when used in this specification, specify the presence ofstated features, integers, steps, operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, integers, steps, operations, elements, components,and/or groups thereof.

As used herein, the term “if” is, optionally, construed to mean “when”or “upon” or “in response to determining” or “in response to detecting”or “in accordance with a determination that,” depending on the context.Similarly, the phrase “if it is determined” or “if [a stated conditionor event] is detected” is, optionally, construed to mean “upondetermining” or “in response to determining” or “upon detecting [thestated condition or event]” or “in response to detecting [the statedcondition or event]” or “in accordance with a determination that [astated condition or event] is detected,” depending on the context.

The foregoing description, for purpose of explanation, has beendescribed with reference to specific embodiments. However, theillustrative discussions above are not intended to be exhaustive or tolimit the scope of the claims to the precise forms disclosed. Manymodifications and variations are possible in view of the aboveteachings. The embodiments were chosen in order to best explain theprinciples underlying the claims and their practical applications, tothereby enable others skilled in the art to best use the embodimentswith various modifications as are suited to the particular usescontemplated.

What is claimed is:
 1. A photon detector, comprising: a substrate; afirst waveguide configured to guide photons from a photon source, thefirst waveguide having a first linear coupling region and respectiveportions on each side of the first linear coupling region, wherein thefirst linear coupling region has a first length; a second waveguide thatis distinct and separate from the first waveguide, the second waveguidehaving a second linear coupling region that is optically-coupled to thefirst linear coupling region of the first waveguide, wherein the firstlinear coupling region of the first waveguide is a first distance fromthe second waveguide, and the respective portions of the first waveguideon each side of the first linear coupling region are further from thesecond waveguide than the first linear coupling region; and asuperconducting detector component configured to detect photons withinthe second waveguide, the superconducting detector component having alinear detector portion positioned adjacent to, and optically-coupledwith, the second linear coupling region, wherein the linear detectorportion has a second length that is longer than the first length, andthe linear detecting portion spans the second linear coupling region;wherein the first waveguide and the second waveguide are integrated onthe substrate.
 2. The detector of claim 1, wherein the superconductingdetector component detects photons in part by transitioning from asuperconducting state to a non-superconducting state in response toreceiving light having an intensity above a threshold intensity.
 3. Thedetector of claim 1, further comprising one or more electrical contactselectrically connected to the superconducting detector component andoptically decoupled from the second waveguide.
 4. The detector of claim1, wherein the linear detector portion is adapted to have a uniformcurrent density.
 5. The detector of claim 1, wherein the first waveguideand the second waveguide are positioned and sized to enable light toadiabatically transfer from the first waveguide to the second waveguide.6. The detector of claim 1, wherein the first waveguide and the secondwaveguide are positioned and sized to enable light to evanescentlytransfer from the first waveguide to the second waveguide.
 7. Thedetector of claim 1, wherein the first waveguide and the secondwaveguide are configured to have a preset light transfer rate betweenthe first and second waveguides.
 8. The detector of claim 1, wherein atleast one of the first linear coupling region and the second linearcoupling region has a tapered width.
 9. The detector of claim 1, furthercomprising: a third waveguide that is distinct and separate from thefirst waveguide and the second waveguide and optically-coupled to thefirst waveguide; and a second superconducting component positionedadjacent to the third waveguide and configured to detect photons withinthe third waveguide.
 10. A method for detecting photons, the methodcomprising: receiving one or more photons from a photon source;directing the one or more photons through a first waveguide wherein thefirst waveguide has a first linear coupling region and respectiveportions on each side of the first linear coupling region; transferringat least one photon of the one or more photons from the first linearcoupling region of the first waveguide to a second linear couplingregion of a second waveguide that is distinct and separate from thefirst waveguide, wherein the first linear coupling region has a firstlength, the first waveguide and the second waveguide are integrated on asingle substrate, the first linear coupling region of the firstwaveguide is a first distance from the second waveguide, and therespective portions of the first waveguide on each side of the firstlinear coupling region are further from the second waveguide than thefirst linear coupling region; and detecting the at least one transferredphoton within the second waveguide using a photon sensor having a lineardetecting portion positioned adjacent to the second linear couplingregion, wherein the linear detecting portion has a second length that islonger than the first length, and the linear detecting portion spans thesecond linear coupling region.
 11. The method of claim 10, whereintransferring at least one of the photons from the first waveguide to thesecond waveguide comprises transferring a preset ratio of the one ormore photons to the second waveguide.
 12. A directional coupler device,comprising: a substrate; a first photonic waveguide including a firstregion and a second region that is distinct from and mutually exclusiveto the first region of the first photonic waveguide, wherein the firstregion of the first photonic waveguide has a linear shape with a firstend and a second end that is opposite to the first end of the firstregion of the first photonic waveguide; and wherein the first region ofthe first photonic waveguide is configured to receive one or morephotons travelling from the first end of the first region of the firstphotonic waveguide toward the second end of the first region of thefirst photonic waveguide; a second photonic waveguide that is distinctand separate from the first photonic waveguide, the second photonicwaveguide including a first region and a second region that is distinctfrom and mutually exclusive to the first region of the second photonicwaveguide; wherein the first region of the second photonic waveguide islinear in shape and positioned adjacent to the first region of the firstphotonic waveguide; wherein the first region of the second photonicwaveguide is a first distance from the first photonic waveguide, and thesecond region of the second photonic waveguide is a second distance tothe first photonic waveguide, that is greater than the first distance;wherein the first region of the second photonic waveguide has a firstend and a second end that is opposite to the first end of the firstregion of the second photonic waveguide; and whereby at least a subsetof the one or more photons transmitted from the first end of the firstregion of the first photonic waveguide toward the second end of thefirst region of the first photonic waveguide is transferred to thesecond photonic waveguide; and a superconducting detector componenthaving a first portion and a second portion that is distinct from andmutually exclusive to the first portion of the superconducting detectorcomponent; wherein the first portion of the superconducting detectorcomponent is linear in shape and positioned adjacent to the first regionof the second photonic waveguide; wherein the first portion of thesuperconducting detector component spans the first region of the secondphotonic waveguide; and whereby at least a portion of the first portionof the superconducting detector component transitions from asuperconducting state to a non-superconducting state in response to oneor more incident photons transmitted from the first photonic waveguide;wherein the first photonic waveguide and the second photonic waveguideare integrated on the substrate.
 13. The device of claim 12, wherein thefirst portion of the superconducting detector component is longer thanthe first region of the first photonic waveguide.
 14. The device ofclaim 12, wherein the first region of the first photonic waveguide isphase matched with a combination of the first region of the secondphotonic waveguide and the first portion of the superconducting detectorcomponent.
 15. The device of claim 12, wherein the first region of thefirst photonic waveguide has a first width and the first region of thesecond photonic waveguide has a second width that is more or less thanthe first width.
 16. The device of claim 12, wherein the first portionof the superconducting detector component is vertically stacked with thefirst region of the second photonic waveguide.
 17. The device of claim12, further comprising a first layer that includes both the first regionof the first photonic waveguide and the first region of the secondphotonic waveguide.
 18. The device of claim 12, further comprising areadout circuit configured to measure a resistance of at least the firstportion of the superconducting detector component.
 19. The device ofclaim 12, further comprising a current source configured to provide afirst current to the first portion of the superconducting detectorcomponent.
 20. The device of claim 12, wherein the second region of thefirst photonic waveguide is not optically coupled with the first orsecond region of the second photonic waveguide.